In the transfer of liquids from a source to a desired receptacle at a more or less remote location, unusual challenges are presented when the liquid to be transferred is not of uniform composition, has insoluble contaminants or is comprised of suspended solids that tend to settle out of solution. The situation is exacerbated when pump cycles are discontinuous and the pump is idle long enough to allow sediment to clog pump internal moving parts. In most applications, it is impractical to flush the transfer lines and pump components between pump cycles. Similar problems arise even when solids are comminuted or when viscosity is great enough to cause stress on moving pump components. One particularly vexing problem is the tendency for some solutions of otherwise perfectly soluble chemicals to precipitate crystals which clog outlets and interfere with the operation of ball values, spring leaded check valves, and the like.
The type of pump selected for a particular application is dictated by the nature of the application. Selection must take into account both the mechanism propelling liquid, but also the design of the valves creating the unidirectional flow. For example, the bellows-type component of the instant pump is an excellent source of measurement and propulsion, but if conventional duckbill valves are employed, especially in vertical orientation, the cavities surrounding the duckbill quickly plug, and the valve will not open.
In general, conventional valves of the paddle, vane, or flexible vane type are not suitable for transferring liquids having high sediment content. Between pump cycles, sediment accumulates on the floor of the valve impeding flow in subsequent cycles. Even the flexible vane embodiment, while avoiding complete plugging because of flexing over sediment deposits, nevertheless will give inaccurate delivery volumes if relying on lapsed time records, and would require real time volumetric determinations.
U.S. Pat. No. 4,445,823 discloses a transfer system for manure and other barn waste (one of the applications to which the present invention is particularly well suited). It describes a powered shaft upon which is mounted a hollow piston urged up and down in a collection hopper to effect agitation and create a pumping action. Although much of the transfer flow is affected by gravity, agitation is beneficial in that it largely prevents a heavy scum from forming on the surface of the liquid, and also prevents stagnation in the upper levels of the hopper.
Another approach to pumping heterogeneous liquids is disclosed in U.S. Pat. No. 4,773,834, and consists of a screw-like transfer of materials in a feedstock through a progressive cavity pump. The screw has helical continuous depressions sealed by a pliant filler contained within a rigid housing. Material is moved by rotating the screw in an upwardly direction to physically translate the material from the entry to the exit point. This device is suitable for conveying both mixed content liquids as well as dry solids. A still further approach is disclosed in U.S. Pat. No. 7,553,124 for a centrifugal pump having one or two recessed impellers; or one or two-disk type impellers, or a combination of one recessed and one disk-type. The pump is designed for high viscosity liquids, slurries, and liquids with solids. One advantage is a lack of dead space in the pump chamber. U.S. Pat. No. 7,321,753 describes an interesting secondary pumping device in which a bladder is contained within a housing chamber in which both contain liquids. When the housing reservoir is filled, the bladder is squeezed thereby expelling the liquid contained therein.
There are many patents disclosing liquid transfer systems, i.e., for example, U.S. Pat. Nos. 8,186,817 and 6,733,252. Such patents disclose functional sites and conduit strategies, as well as transfer stations, but provide few details of the pumping equipment specifications.